1. Field of the Invention
The present invention relates to covers for receptacles and more particularly to a heated cover which reduces evaporative loss of a material held in a receptacle and a device for placing and removing the cover on the receptacle.
2. Description of Related Art
Some materials, in liquid or solid form, will gradually evaporate even at a relatively low temperature such as room temperature. The rate of evaporation is dependent in part on the volatility of the material, the temperature of the material and the environment to which the material is exposed. Unless evaporation is purposely intended, evaporation of material is generally undesirable since the evaporation process involves a loss of material and a change in the concentration of the material remaining in the container.
Evaporation from an open container can be reduced to some extent by covering the opening of the container. However, in situations when a small amount of material is left in a container for a prolonged period of time, for example, repeated heating during DNA sequencing reactions, the rate of evaporation is too rapid for the small amount of sample available even with the container covered. Furthermore, the evaporated material tends to condense and adhere onto the cool underside of a cover. Thus, the volume of material in the container is being reduced both by evaporation and condensation because the condensate which adheres to the cover will be removed from the container when the cover is lifted away. Moreover, for a mixture of different types of materials, the overall concentration of the mixture components remaining in the container will change as a result of evaporation. It is important in some situations to maintain a constant concentration, such as in DNA sequencing reaction processes.